int MPI_Bsend(const void *buf, int count, MPI_Datatype datatype, int dest, int tag,
MPI_Comm comm)
In deciding how much buffer space to allocate, remember that the buffer space is not available for reuse by subsequent MPI_Bsends unless you are certain that the message has been received (not just that it should have been received). For example, this code does not allocate enough buffer space
MPI_Buffer_attach( b, n*sizeof(double) + MPI_BSEND_OVERHEAD );
for (i=0; i<m; i++) {
MPI_Bsend( buf, n, MPI_DOUBLE, ... );
}
because only enough buffer space is provided for a single send, and the
loop may start a second MPI_Bsend before the first is done making use of the
buffer.
In C, you can force the messages to be delivered by
MPI_Buffer_detach( &b, &n );
MPI_Buffer_attach( b, n );
(The MPI_Buffer_detach will not complete until all buffered messages are
delivered.)
This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.
All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.
All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.